Magnetic polaron formation of localized excitons in semimagnetic semiconductor alloys of Cd0.8Mn0.2Te

Itoh, Tadashi; Komatsu, Eiichi

doi:10.1016/0022-2313(87)90124-4

Cited by 32 publications

(30 citation statements)

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“…In turn, these aligned local moments act back on the exciton's spin, which lowers the exciton's energy, further localizes the exciton, and further stabilizes the polaron. The stability and binding energy of EMPs therefore depends on the detailed interplay between many factors including the exciton lifetime, the polaron formation time, the exchange field B ex , sample dimensionality, and temperature.EMPs and collective magnetic phenomena have been experimentally studied in a variety of Mn 2+ -doped semiconductor nanostructures, including CdMnSe and CdMnTe-based epilayers and quantum wells [34][35][36][37][38][39][40][41][42], selfassembled CdMnSe and CdMnTe quantum dots grown by molecular-beam epitaxy [14][15][16][18][19][20][21][22][23][24][25], and most recently in CdMnSe nanocrystals synthesized via colloidal techniques [8,28]. Common measurement techniques include the analysis of conventional (i.e., non-resonant) PL [8, 14, 15,18,21,28,39] and time-resolved PL [8, 16,28,34,35,40].…”

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Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

et al. 2017

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In semiconductors, quantum confinement can greatly enhance the interaction between band carriers (electrons and holes) and dopant atoms. One manifestation of this enhancement is the increased stability of exciton magnetic polarons in magnetically-doped nanostructures. In the limit of very strong 0D confinement that is realized in colloidal semiconductor nanocrystals, a single exciton can exert an effective exchange field Bex on the embedded magnetic dopants that exceeds several tesla. Here we use the very sensitive method of resonant photoluminescence (PL) to directly measure the presence and properties of exciton magnetic polarons in colloidal Cd1−xMnxSe nanocrystals. Despite small Mn 2+ concentrations (x=0.4-1.6%), large polaron binding energies up to ∼26 meV are observed at low temperatures via the substantial Stokes shift between the pump laser and the resonant PL maximum, indicating nearly complete alignment of all Mn 2+ spins by Bex. Temperature and magnetic field-dependent studies reveal that Bex ≈ 10 T in these nanocrystals, in good agreement with theoretical estimates. Further, the emission linewidths provide direct insight into the statistical fluctuations of the Mn 2+ spins. These resonant PL studies provide detailed insight into collective magnetic phenomena, especially in lightly-doped nanocrystals where conventional techniques such as nonresonant PL or time-resolved PL provide ambiguous results.Advances in the colloidal synthesis of magneticallydoped nanomaterials have sparked a renewed focus on low-dimensional magnetic semiconductors [1][2][3][4][5][6][7][8]. The interesting magnetic properties of these materials originates in the strong sp-d exchange interactions that exist between carrier spins (i.e., band electrons and holes with s-and p-type wavefunctions) and the local 3d spins of embedded paramagnetic dopant atoms such as Mn, Co,. At the microscopic level, the strength of this interaction for a dopant located at position r i scales with the probability density of the carrier envelope wavefunctions at that point: |ψ e,h (r i )| 2 . As such, local spin-spin interactions can be greatly enhanced by strong quantum confinement, which compresses carrier wavefunctions to nanometer-scale volumes and therefore increases |ψ e,h (r)| 2 . The extent to which these exchange interactions can be enhanced and controlled via quantum confinement is an area of significant current interest and has recently been studied in a variety of magnetically-doped semiconductor nanostructures, including nanoribbons [12, 13], nanoplatelets [14], epitaxial quantum dots [14][15][16][18][19][20][21][22][23][24][25][26], and colloidal nanocrystals [1-8, 27, 28, 30].A particularly striking consequence of sp-d interactions in II-VI semiconductors is the formation of exciton magnetic polarons (EMPs), wherein the effective magnetic exchange field from a single photogenerated exciton -B ex -induces the collective and spontaneous ferromagnetic alignment of the magnetic dopants within its wavefunction envelope, generating a net local...

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“…Common measurement techniques include the analysis of conventional (i.e., non-resonant) PL [8, 14, 15,18,21,28,39] and time-resolved PL [8, 16,28,34,35,40].…”

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Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

et al. 2017

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“…Thus, the diffusion model [7] is in conflict with the experimental findings [1][2][3][4], as they point to the exponential dependence of E p on t.…”

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“…

Consider a carrier trapped at t = O in a localized state.

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“…Progress in the application of short light pulses for monitoring of dynamical processes has made it possible to trace the emerging of exciton magnetic polarons (EMP) after optical injection of carriers across the band gap in diluted magnetic semiconductors (DMS) [1][2][3][4][5][6]. In this paper we discuss mechanisms which might account for the fast dynamics of the polaron formation in DMS.…”

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Formation Time of Magnetic Polarons

et al. 1995

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It is shown that non-scalar spin-spin interactions rather than spinlattice coupling or spin diffusion control the dynamics of the magnetization formation visible in time-resolved luminescence and SQUID magnetometry.PACS numbers: 78.55.Et, 75.50.Rr Progress in the application of short light pulses for monitoring of dynamical processes has made it possible to trace the emerging of exciton magnetic polarons (EMP) after optical injection of carriers across the band gap in diluted magnetic semiconductors (DMS) [1][2][3][4][5][6]. In this paper we discuss mechanisms which might account for the fast dynamics of the polaron formation in DMS.Consider a carrier trapped at t = O in a localized state. Its adiabatic wave function is described by a Schródinger equation which contains: (i) kinetic energy, taken here in the one-band effective-mass approximation, (ii) potential energy that includes the localizing and confining potential, (iii) a nonlinear term HM = HM(r, t), which describes the exchange interaction with the time-dependent polarization of the surrounding localized spins, Here J = α or Q is the electron-or hole-magnetic ion exchange integral, while g and M0 (H) denote the Lande factor and the equilibrium magnetization of the localized spins, respectively. The molecular field H* produced by the carrier and experienced by the ionic spins appears at t = 0, and is then given by Finally, G(r, t) is the response function of the spins. As a starting point we assume that it can be described by Bloch equations with the diffusion term included.

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High‐density selective excitation effect on excitons in semimagnetic semiconductor CdMnTe

Katayama¹,

Miyajima²,

Ashida³

et al. 2006

Physica Status Solidi (b)

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Many body effects among electron -hole pairs and exchange interaction of spins between electron/hole and Mn 2+ ions have been investigated in a semimagnetic semiconductor of CdMnTe under the selective excitation of high-density localized excitons with use of a picosecond pulse laser. A new nonlinear luminescence band (X band) has been found on the high-energy side of conventional exciton magnetic polaron band and its peak energy shows a pronounced red shift with the increase of excitation power and/or with the application of magnetic field. Time-resolved luminescence without magnetic field has revealed the characteristic behaviour of the X band with a longer rise time for the higher energy side. However, this tendency disappears with the application of magnetic field. As the origin of the X band, we propose the high-density spin-polarized electron -hole pairs interacting with microscopic Mn 2+-ion spins aligned through the exchange interaction.

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Magnetic polaron formation of localized excitons in semimagnetic semiconductor alloys of Cd0.8Mn0.2Te

Cited by 32 publications

References 5 publications

Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

Formation Time of Magnetic Polarons

High‐density selective excitation effect on excitons in semimagnetic semiconductor CdMnTe

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Magnetic polaron formation of localized excitons in semimagnetic semiconductor alloys of Cd0.8Mn0.2Te

Cited by 32 publications

References 5 publications

Direct Measurements of Magnetic Polarons in Cd1–xMnxSe Nanocrystals from Resonant Photoluminescence

Direct Measurements of Magnetic Polarons in Cd1–xMnxSe Nanocrystals from Resonant Photoluminescence

Formation Time of Magnetic Polarons

High‐density selective excitation effect on excitons in semimagnetic semiconductor CdMnTe

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Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence

Direct Measurements of Magnetic Polarons in Cd_1–xMn_xSe Nanocrystals from Resonant Photoluminescence